Bipolar electrolysis cells with mercury cathode and having novel amalgam splitting vessel

ABSTRACT

Disclosed is a bipolar, mercury cathode, electrolytic cell for the electrolysis of brine. Mercury amalgam is removed from each individual cell through separate lines and fed to a mercury amalgam splitter. Mercury amalgam splitter contains a separate compartmentalized wheel for each inlet stream of amalgam. The compartmentalized wheel is caused to rotate and to drop the mercury from separate streams of different electrical potentials into a common mercury pool at a single potential. The mercury pool is electrically insulated from separate streams.

United States Patent Raetzsch et al.

151 3,657,098 [451 Apr. 18, 1972 BIPOLAR ELECTROLYSIS CELLS WITH MERCURYCATHODE AND HAVING NOVEL AMALGAM SPLITTING VESSEL Carl W. Raetzsch; JohnF. Van Hoozer; Hugh Cunningham, all of Corpus Christi,

Inventors:

Tex.

Assignee: PPG Industries, Inc., Pittsburgh, Pa. Filed: Jan. 31, 1969Appl. No.: 795,665

Related U.S. Application Data Division of Ser. No. 410,579, Nov. 12,1964, abandoned.

U.S. Cl ..204/2l9, 204/220, 204/250,

204/268 Int. Cl. ..C22d 1/04, BOlk 3/00 Field of Search ..204/2l9,220,250, 268

[56] References Cited UNITED STATES PATENTS 3,400,055 9/1968 Messner..204/220 X Primary Examiner-John H. Mack Assistant Examiner-D. R.Valentine Attorney-Chisholm and Spencer [5 7] ABSTRACT Disclosed is abipolar, mercury cathode, electrolytic cell for the electrolysis ofbrine. Mercury amalgam is removed from each individual cell throughseparate lines and fed to a mercury amalgam splitter. Mercury amalgamsplitter contains a separate compartmentalized wheel for each inletstream of amalgam. The compartmentalized wheel is caused to rotate andto drop the mercury from separate streams of different electricalpotentials into a common mercury pool at a single potential. The mercurypool is electrically insulated from separate streams.

1 Claims, 12 Drawing Figures PATENTEDAPR 18 1912 sum 2 OF 9 INVENTORSCARL w. EAETZSCI'I Jul/N )5 WW 1100252, BY #06 CUNNINGHAM MAM! Arm/awayPATENTEDAPRWIBYZ 3,657,098

SHEET 70F 9 zl 5 g 6 5 2 m 3 g V i 0 J I U FNIIO'IHQ i X INVENTOR.

CHRL W. fiAfiTZSCH JOHN F. VAN 1/00 zen, Q1 BY H H C NNINGHHM BIPOLARELECTROLYSIS CELLS WITH MERCURY CATI-IODE AND HAVING NOVEL AMALGAMSPLITTING VESSEL This application is a division of our copendingapplication Ser. No. 410,579, filed Nov. 12, 1964, now abandoned.

The present invention relates to electrolytic cells. More particularly,the present invention relates to electrolytic cells for the electrolysisof alkali metal chloride solutions. Still more particularly, the presentinvention relates to electrolytic cells for the electrolysis of alkalimetal chloride solutions of the flowing mercury cathode type. 1

In the manufacture of elemental chlorine and caustic soda by theelectrolysis of alkali metal chloride solutions, it has becomeincreasingly important that caustic soda of high purity be obtainedduring such electrolysis. This is particularly true with respect tocaustic soda produced for use in the textile industry, and thus inrecent years, demand for high grade, ironfree caustic soda has increasedtremendously. Caustic soda with these qualifications can be madedirectly in electrolytic cells having a flowing mercury cathode. Whilediaphragm cell caustic can be purified to a satisfactory extent for usein the textile industry, purification procedures are costly andcomplicated, giving rise to an increased demand for caustic sodaproduced in the flowing mercury cathode cell where the need for suchcomplicated and expensive purification systems are not existent. Forthis reason, the trend in the chlorine-alkali industry for the pastseveral years has been to manufacture more and more chlorine and causticsoda in mercury cells as opposed to diaphragm cells.

Normally mercury cells operate at slightly higher voltages thandiaphragm cells. This higher voltage is due in part to the fact thatthey are operated at high current densities. High current densities areemployed to utilize the cell anodes to a maximum degree since theyrequire a considerable quantity of floor space. Mercury cells require aflowing mercury cathode. Anodes are typically positioned above thiscathode to provide an electrolytic surface for decomposing brine whichis caused to flow between the anode and cathode. Thus, the minimum cellroom floor space required for a given cell is at least equal to the areaof the anode of the cell utilized. Since the cells themselves arerelatively large in comparison to diaphragm cells, mercury cellinstallations often require excessively large cell room space in whichto operate.

In accordance with the present invention, a novel electrolytic alkalimetal-chlorine cell is provided which requires a minimum amount of floorspace for successful operation and provides an extremely largeelectrolytic surface area for electrolysis to take place per unit areaof floor space. None of the anode adjustments typically encountered inmercury cell operation are required with this cell. In addition, thecell may be operated at lower current densities than conventionalmercury cells without suffering the penalty of excessive floor spacerequirements while achieving high productivity per cell. This, ofcourse, reduces electrical energy consumption. Bus bar requirements forelectrical connection to the cells of this invention are drasticallyreduced over those necessary for a conventional mercury cell circuit.Further, piping requirements for feed to the cell and removal of productare minimized.

For a more complete understanding of the present invention, reference ismade to the accompanying drawings in which:

FIG. 1 represents a side elevation of the bipolar mercury cell of theinstant invention showing an anode half cell, a cathode half cell, andan intermediate cell unit having an anode and a cathode disposed betweenthe top half cell and the bottom half cell of the bipolar mercury cellshown.

FIG. 2 is a plan view, partially in perspective, with the cover brokenaway to show the anode member of the anode half cell and the cathodetray or surface of the intermediate cell unit positioned above thecathode of the bottom half cell, and indicating the flow of brine andmercury.

FIG. 3 is a cross-section of the cell of FIG. 2 taken along lines I-I ofFIG. 2, the center section being partially omitted, showing the chlorineoutlet and one modification of the anode attachment and electricalconnection to the anode.

FIG. 4 is a cross-section of the cell taken along lines Il-II of FIG. 2the center section being partially omitted, showing the anode half cellof the cell assembly, the cathode half cell of the cell assembly, andthe intermediate cell unit, and showing in detail the mercury inlet andoutlet and the relationship of the brine and the mercury within thecell.

FIG. 5 is a perspective view partially in section of the mercury inlet29 of the bottom half cell of the cell assembly shown in FIG. 2.

FIG. 6 is a cross-section of the mercury feed splitter 15 shown in FIG.1.

FIG. 7 is a cross-section of the amalgam splitter 35 of FIG. 1, takenalong the mid line III-III of FIG. 1.

FIG. 8 is a section of the amalgam splitter 35 of FIG. I taken alonglines IV-IV showing the details of the lining of the splitter.

FIG. 9 is a cross'section of the amalgam denuder 37 of FIG. 1, takenalong the mid line V-V.

FIG. 10 is a cross-section of the cell of FIG. 2 with the centerpartially omitted taken along the line I-I, and having a furtherembodiment of the anode support member of the cell in lieu of thesupport shown in FIG. 2.

FIG. 11 is a cross-section along lines II-II of the cell of FIG. 2 withthe center partially omitted and showing the anode support modificationof FIG. 10 in lieu of the anode support member of FIG. 2.

FIG. 12 is a further embodiment of a mercury splitter which may be usedin lieu of splitter 15 shown in FIG. 1.

Turning now to the drawings, with particular reference to FIGS. 1, 2, 3,and 4, there is shown a bipolar flowing mercury cathode alkali-chlorinecell in which, for illustrative purposes, two cells have been shown. Asseen in FIG. 1, the cells are composed of an upper anode containingcover member on anode half cell 1 and a cathode containing bottom memberon cathode half cell 8. Intermediate the cover member 1 and the bottommember 8 is disposed a bipolar cell unit generally indicated as 7 whichcontains on its upper surface a tray 9 for the reception of the mercurycathode and on its bottom side an anode 10 to be used in conjunctionwith the mercury contained in tray 11 of the bottom member 8. The covermember 1 is lined with a suitable insulating material such as rubber andthe lining 6 protects the underside of the cover 1 and electricallyinsulates it partially from the cell unit 7 placed below it. The covermember 1 is composed of a back up plate 12 of steel or other suitableelectrically conductive structural metal. The backer plate 12a containstapped holes 18 and 18 (See FIG. 3) which are plugged on their uppersurface with plugs 19 and 19' and contain within the holes bolts 34 and34'. The plugs 19 and 19 may be omitted it desired. Operation of thecell without plugs 19 and 19' has been accomplished and some slightimprovement in electrical conductivity observed with no deleteriouseffects encountered. In such an operation the bolts become covered withmercury which apparently assists in conducting current through the boltsfrom the cell above. These bolts are affixed to and hold in placeagainst the back plate 12a a titanium sheathed electrically conductiverod member 13a preferably constructed of copper or aluminum. Thetitanium sheath 14 is intimately afirxed to the rod member by suitablebinding material or mechanically attached by compression against the rodso that maximum electrical conductivity between the two metals isrealized. The anode 17 of the cell cover 1 is affixed to the titaniumsheath 14 such as by welding and when in place is positioned above thetray 9 of the cell unit 7. Affixed to the outer surface of the covermember I is a suitable bus-connector 2 which, during operation of thecell, is suitably bolted to the cell room bus bars (not shown). Severalorifices are shown in the cover member of the cell, which orifices areutilized for the performance of certain functions. Thus, in FIG. 2, twoorifices 4 and 4 are shown which are utilized as chlorine gas collectionpoints or conduits. Orifices 5 and 5 are utilized for the introductionof brine into the cell, as indicated in FIGS. land 2.

In the over-all operation of the cell, as seen looking at FIG. 1,mercury is introduced into the cell by dropping it into the mercurysplitting device 15. The mercury splitting device contains a rotatingmember generally indicated at which rotates on a vertical axis and has anozzle member 21 attached on the undersurface thereof which constantlyemits a flowing stream of mercury. As the device rotates, it passes adividing member 22 and the mercury is divided into two separatereservoirs 23 and 24. The contents of reservoir 23 are fed through line25 to a mercury distributor 27. The contents of reservoir 24 are fedthrough line 26 to a mercury distributor 29. The mercury passes fromdistributors 27 and 29 across the faces of the trays 9 and 11respectively (See FIG. 4) and flows to the opposite end of the cell.Brine is continuously introduced through brine feed inlets 5 and 5during this operation and passes from the upper tray 9 to the lower tray11 in a manner to be described hereinafter. Current is applied to thecell and electrolysis takes place between the face of the anodes 17 and10 and the surface of the mercury cathode flowing across the cell intrays 9 and 11. Elemental chlorine formed during the electrolysis isremoved from the cell through chlorine outlets 4 and 4 in a manner to bedescribed hereinafter. Sodium-mercury amalgam is formed during theelectrolysis on the flowing mercury cathode as it passes across the celland is collected in the cell in the collection sumps 30 and 31. Thus,the contents of tray 11 collect in sump 31 and those of tray 9 in sump30. The amalgam in sump 30 is introduced into an amalgam splitter 35through line 32. The amalgam in sump 31 is introduced into splitter 35through line 33. After passing through the splitter, the amalgam ispassed through line 36 to the mercury denuder 37. In the denuder 37 theamalgam is contacted with water introduced through line 38, and thecaustic soda product is removed through line 39. Hydrogen evolved duringthe denuding operation is removed from the denuder through line 40. Thedenuded mercury is removed through line 41 and is pumped by means ofpump 43 through line 41' to the mercury feed splitter 15, and theprocess is repeated. Depleted brine is removed from the cell throughline 42 after having collected in sump 44. It is, of course, to beunderstood that the depleted brine removed from the cell may beresaturated and utilized once more in the cell in accordance withconventional practices in the art. The cell is supported on posts 45 and46 which are anchored to the floor of the cell room on footers 47 and48.

In accordance with the teachings of this invention, the mercury flows ina longitudinal direction across the cell, as shown in FIG. 2. Preferablythe brine flows tangentially to the flow of mercury in the first cellunit to a brine down-comer 49. This brine then reverses its flow on thenext lower tray and flows in the opposite direction, but stilltangential to the flow of mercury in that tray. The mercury flow in allthe trays is preferably in the same direction. Thus, as shown in FIGS. 2and 5, the mercury introduced through lines 25 and 26 enters mercuryfeed distributors 27 and 29, respectively. As shown in more detail inFIG. 5, which is an enlarged perspective view of the mercury feeddistributor 29, this unit contains an elongated slot 50 on its side sothat the mercury, when it reaches the level of the slot, flows out ofthe distributor and across the tray 11 associated with that distributor.An identical configuration of the mercury distributor is contained inthe unit 27 of FIG. 2 so that the slotted device constantly provides afilm of mercury across the tray 9 with which that distributor isassociated. As will be understood by those skilled in the art, the traysthemselves are tilted downwardly from the mercury feed point to thecollection point or sumps 30 and 31 so that the mercury will flow bygravity from the feed point to the sumps or collection points 30 and 31.Located on the side of the trays between each cell tray are housings 51,52, 53, and 54. Contained in each of these housings is an adjustingscrew element 55 which rests on an insulated member 56 of the unitimmediately below. Suitable electrical insulation, such as micarta, maybe employed for this purpose so long as it provides adequate insulationto prevent shorting caused by the differences in potential between thevarious cell units associated with each of the housing members. Theseadjustable screw elements are utilized to provide a proper slope for theflowing mercury between the various cell units employed and to provide ameans for adjusting the level of the mercury across the width of thecell to thereby insure uniform distribution of mercury across the widthof the cell.

Turning now to FIG. 3, the details of the construction and theelectrical connection to the cell anodes can be readily seen. In FIG. 3there is shown the cell cover member generally indicated as 1 whichshows two drilled holes 18 and 18' in the back up plate 12 suitablyplugged with plug members 19 and 19. Located immediately below the plugare bolt elements 34 and 34 which have affixed thereto rod members 13and 13', preferably constructed of copper and sheathed in a titaniumtube or sheath l4 and 14' respectively. The copper rods encased intitanium are sheaths curved at the bottom into a fiat member which iswelded to a platinized titanium anode member 17. Thus, the titaniumencased copper rods serve as support members for the anode 17 as well asmeans for distributing current thereto. The mercury contained within thecell, generally indicated by the numeral 38, flows beneath the anodemember 17 on a steel tray 9 which, at its peripheral edges, is bonded toa rubber lining 58 of the cell unit 7. The base member 12a of the tray 9serves as the back plate for the next anode and conducts the electricalcurrent from the cathode of the first cell to the current distributor13a of the next adjacent cell unit which is located immediately below itand like rod 13 is also encased in a titanium sheath. The insulation 58and the presence of gasket 60 serves to protect the cell above fromshorting out with the cell below. The chlorine from the bottom cellrises up through the brine down-comer 49 as brine from the upper trayfalls downwardly through the down-comer 49 in countercurrent contacttherewith. Gaseous chlorine ultimately escapes from the cell throughoutlet 4 located in the cover member 1 of the cell. While in the drawingof FIG. 3 only a single unit of attachment to the cell anode is shown,it is, of course, understood that a plurality of these units extendacross the cell to provide adequate support for the flat platinizedtitanium anode and prevent it from warping during operation. A gasket 59is placed between the cover member or upper anode containing member ofthe cell and the tray 9, and a similar gasket 60 is located between thecell unit 7 and the bottom 8 of the cell. These gaskets serve toinsulate and seal one cell from the other during operation. To the sideof the cell and underneath the adjusting screw member 55 is a nut 61which is affixed in place when proper adjustment of the slope of thecell trays has been made.

Turning to FIG. 4, there is shown the relationship of the electricalsupport members or rods 13 to the anodes 17, as well as the relationshipof rods 13a to the cell unit anode 10. In addition, the positioning ofthe mercury feed reservoirs 27 and 29 and the mercury-amalgam sumps 30and 31 of the cell are also depicted. The mercury cell distributors 27and 29 are bolted to the ends of each tray by suitable tapped bore holes62 in the cell trays 9 and 11 respectively. These tapped bore holes 62are provided with bolt elements 64 and the entire units are thus boltedto the cell trays 9 and 11.

As shown in FIGS. 4 and 5, the mercury distributor 29 consists of twoside members 66 and 67; a bottom member 68 and a top member 69 whichdefine a hollow cavity 70. The side member 66 which abuts against thecell tray 11 is slotted at 50 on its long axis so as to be open to thetray 11 with which this distributor 29 is associated. The distributor 29is also provided with a slotted channel 71 in the vertical directionwhich channel 71 communicates with the long axis slot 50 and a cavity 72at the bottom end. Cavity 72 runs parallel to slot 50 along the longaxis of the distributor 29. Thus, mercury introduced through line 26into the cavity 72 traversing the long axis of the distributor 29 risesthrough the vertical slot or channel 71 to the chamber 70 and fromthere, by virtue of the slot 50 communicating with the tray 11, mercuryis introduced into the cell tray 11 and flows across the tray and theface of the anode placed above the tray. If desired, cavity or channel72 may be provided with a plurality of drilled holes in lieu of thevertical channel 71 so that a plurality of spaced channels are providedinstead of a unitary slot. Similarly channel 72 may be a pipe having aplurality of openings on its upper surface at spaced intervals whichcommunicate with a plurality of spaced vertical holes. Such spaced holewould of course terminate in the chamber 70 in this case as does thevertical slot 71. The mercury, as mercury amalgam, as it reaches theopposite end of the cell, enters the sump 31 formed by the side 73, topmember 74, and bottom member 76. The mercury, as it enters this chamber,settles through a vertical slot 77 into a small reservoir member 78 andis ultimately removed from the cell. This mercury collection or amalgamcollection member or sump 31 is affixed to the side of the cell as sump30 is attached. Sump 30 is provided with a tapped bore hole 79 locatedin the tray 9 and by utilizing suitable bolts 80 is affixed to tray 9.The mercury distributor 27 is of identical construction to the reservoir29 hereinabove described but as will be obvious, it is associated withtray 9. Similarly, the sump 30 is identical in construction to the sump31 described above but is associated with tray 9.

Turning now to FIGS. 10 and 11, there is shown another modification ofthe anode 17 of the cell cover and anode 10 of the cell unit in whichthe electrical connection and the supporting of the anode isaccomplished by means of metal plates 81 in lieu of the titaniumsheathed copper rods 13 of FIGS. 3 and 4. In this modification, titaniumlugs 82 are affixed to the backing plates 12 and 12a of the anodes ofthe cell cover 1 and cell unit 7 respectively, and have attached to themthrough a suitable screw member 83 a plurality of metal plates 81 and 81which are suitably welded to the upper portion of the anodes 17 and 10.A plurality of these metal plates 81 and 81 are placed across the backof the anodes 17 and 10 to provide suitable electrical distribution tothe face of the anodes 17 and 10 to prevent these anodes from warpingduring cell operation. The relationship of the brine feed lines 5 and 5chlorine outlets 4 and 4, and mercury feed lines and 26 remain the samein this modification, the essential difference between this modificationand those shown in FIGS. 3 and 4 being in the electrical connection tothe anodes 17 and 10. The structure of the distributors 27 and 29, sumpsand 31, and the trays 9 and 11 and all other equipment is essentiallythe same as described with reference to the embodiment shown in FIGS. 3and 4.

Turning now to FIG. 6, the mercury splitter 15 of FIG. 1 is shown incross-sectional detail. This splitting device 15 is comprised of amercury inlet tube 84 which fills a cavity 85 formed in the center ofthe device and which rotates around shaft member 86. Shaft 86 ispositioned in a suitable housing 87 and held firm by washer 88 and nut89. A depending nozzle 21 communicates through a channel 91 with thecavity 85. The nozzle 21 rotates in a chamber 90 formed by the sides 92and 93, and bottom 94 of the splitter 15. The bottom member 94 of thecontainer is divided by a member 22 which rises vertically in the centerof the splitter 15 and serves to equally divide mercury entering throughthe nozzle 21 between chambers 90a and 90b. All portions of the splitter15 which are in contact with the mercury are rubber covered by rubberlinings to provide adequate insulation and assist in breaking theelectrical current between the mercury located in each of the individualsections of the splitter 15. The outlets 25 and 26 of the splitter 15feed the two individual cells shown in FIG. 1 through the distributormembers 27 and 29. While only two feed units are shown feeding two cellsin this figure and in FIG. 1, it is, or course, to be understood that amultiplicity of these cells may be employed, in which case the splitter15 would be divided into a sufficient number of individual feed units toprovide an individual mercury cell feed for each individual mercury cellemployed.

Turning to FIGS. 7 and 8, the sodium-mercury amalgam leaving theelectrolytic cell is introduced into the splitting device 35 of FIG. 1.This device is shown in two sectional views in FIGS. 7 and 8. In FIG. 7,sodium-mercury amalgam leaving the cell through line 32 enters unit 35and is dropped into one of the compartments 96 of the compartmentedwheels 97 and 97. As each compartment 96 becomes filled, on theprinciple of the water-wheel, the mercury amalgam pushes thewater-wheels in a clockwise direction, thus electrically splitting itand dropping it into the sump 98, from which it is removed via outlet 36and introduced into the mercury amalgam denuder 37.

While the wheel 97 can operate on a water-wheel principle, provision maybe made to drive it by coupling shaft member to a suitable motor andbelt arrangement. As with the mercury splitter 15, the number ofcompartmented wheels employed will depend on the number of completecells employed in the completed cell. FIG. 12 shows a further embodimentof the mercury splitter 15 in which there is provided two sumps 106 and107. Sump 106 is associated with a wheel 108 and sump 107 with a wheel109. Wheel 108 is fed through pipe 114 and wheel 109 through pipe 115.The sumps are separated by a wall member 110 and this wall member 110 aswell as the walls of the splitter 35 are lined with a rubber lining 111for insulation purposes. Each sump is provided with an outlet 112 and113 for feed to the mercury reservoirs 27 and 29. Discharge isaccomplished by simple overflow into the open tubes 112 and 113. Theseopen tubes would feed mercury to lines 25 and 26 for ultimate feed toreservoirs 27 and 29 respectively. If desired, of course, bottom feedingcan be employed rather than an overflow type as shown in FIG. 12. Themercury fed to pipes 114 and 115 is typically fed from a holdingtank.(not shown) provided with two discharge orifices located on thebottom or sides, one orifice being connected to each of pipes 114 and115. As with the splitter 15, this device will be provided with sumpsand wheels corresponding to the number of complete cells used in thecell assembly.

The denuder 37 shown in FIG. 9 in cross-section is comprised of a steelshell 99 having a perforated baffle 100 located at the bottom thereofand a water inlet 38. The bottom member 101 of the denuder is providedwith an outlet 41 for the removal of denuded mercury. In the upperportion of the denuder is located an outlet 39 for the removal ofcaustic soda. Sodium amalgam is introduced through pipe 36 to a bafflemember 102 located in the upper portion of the denuder where it flowsdownwardly through a perforated plate member 103 and in contact withgraphite particles 104 located between perforated baffle 100 and thebaffle 102. Hydrogen escapes from the cell through a suitable outlet 40,not shown in FIG. 9.

While the invention has been described with reference to the formationof chlorine and sodium-mercury amalgam from brine, it is of coursepossible to utilize the instant cell to manufacture other alkali metalhydroxides from the corresponding alkali metal chloride solution. Thus,KCl can be readily electrolyzed to produce chlorine andpotassium-mercury amalgam and ultimately potassium hydroxide. Further,while platinum plated titanium has been shown as the preferred anodematerial, other noble metals may be utilized as the anode surface andcan be placed upon other base materials such as tantalum.

While the invention has been described with reference to certainspecific and illustrated embodiments, it is not intended that it be solimited except insofar as appears in the accompanying claims.

We claim:

1. A bipolar electrolytic chlorine cell having a series of bipolar cellunits, means to flow mercury streams along the cathodic tops of saidunits, means to impress an electric potential across the series so thatthe several streams of mercury are at different electric potentials,separate collection means to collect the mercury amalgam at the end ofeach cell box, individual means to feed the collected mercury amalgamfrom said collection means to individual inlets in a mercury amalgamsplitting vessel, said vessel having a separate compartmentalized wheelfor receiving mercury amalgam from each of said inlets positioned abovethe bottom of said vessel, means for turning said compartmentalizedwheels to thereby drop said amalgam from said wheels to the bottom ofsaid vessel, and means for removing mercury amalgam from the bottom ofsaid vessel.

